Processes for the production of petroleum from a petroleum-containing subterranean formation employing an aqueous driving fluid containing a thickening agent are well known.
Oil accumulated within a subterranean formation can be recovered, or produced, through wells from the formation using the natural energy within the formation. However, producing operations deplete the natural energy relatively rapidly. Thus, a large amount of the oil is left in a subterranean formation if only the natural energy is used to produce the oil. This production by depletion of the natural energy is often referred to as primary production. Where natural formation energy is inadequate or has become depleted, supplementary operations, often referred to as secondary recovery operations, are used to improve the extent of oil recovery. In the most successful and widely used supplemental recovery operations, a fluid is injected through an injection means, comprising one or more injection wells. The fluid is passed into the formation, displacing oil within and moving it through the formation. The oil is produced from production means, comprising one or more production wells, as the injected fluid passes from the injection means toward the production means. In a particular recovery operation of this sort, water is employed as the injected fluid, and the operation is referred to as waterflooding. The injected water is referred to as the flooding water as distinguished from the in-situ, or connate, water.
While conventional waterflooding is effective in obtaining additional oil from an oil-containing subterranean formation, it has a number of shortcomings. Foremost among these shortcomings is the tendency of flooding water to "finger" through an oil-containing formation and to bypass substantial portions thereof. By fingering is meant the developing of unstable bulges or stringers which advance toward and into the production means more rapidly than the remainder of the flooding water. Furthermore, the water does not normally displace as much oil in the portions of the formation which it contacts as it potentially is capable of doing. In order to obtain a greater displacement of oil or other hydrocarbonaceous fluids, it has been suggested to increase the viscosity of flooding water.
Past suggestions for increasing the viscosity of flooding water have included incorporating water-soluble thickening additives in the water. Additives that have been suggested for this purpose include a wide variety of naturally occurring gums, sugars, and polymers. Bacterially produced heteropolysaccharides have been especially interesting as an additive for thickening flooding water. Also gels made from heteropolysaccharides have been used.
Clampitt et al. in U.S. Pat. No. 3,908,760 disclosed the use of aqueous mediums comprising new aqueous gels prepared from water and biopolysaccharides in secondary recovery operations for the recovery of oil. Clampitt et al. taught that pH was not controlling, but that higher pH retarded the gelation rate.
U.S. Pat. No. 3,383,307 issued May 14, 1968, teaches Goetz' use of polysaccharides to gel water. A bacteria of the genus Xanthomonas was used. Goetz taught that the gel appeared to be reversible on the addition of strongly alkaline materials such as sodium hydroxide.
Previously, substantially large amounts of polyvalent metal ions were used to effect gel formation. However, use of substantially large amounts of polyvalent ions resulted in making gels of low stability. Therefore, what is needed is a method for rapidly forming gels of greater stability for use in recovering hydrocarbonaceous fluids from subterranean formations.